Electron discharge tube and method of manufacture thereof



Jan. 4, 1966 w. R. WEYANT 3,227,908

ELECTRON DISCHARGE TUBE AND METHOD OF MANUFACTURE THEREOF Filed Dec. so, 1963 Fig/.1.

l V/z 1/4/14 K Wfm/vr United States Patent 3,227,968 ELECTRUN DISCHARGE TUBE AN METHOD OF MANUFACTURE THEREQF William R. Weyant, Nixon, N..l., assignor to Radio Corporation of America, a corporation of Delaware Filed Dec. 3%), 1963, Ser. No. 334,385 3 Claims. (Cl. 313243) This invention relates to electron discharge tubes and particularly to electron discharge tubes having filamentary cathodes and to a novel method of making such tubes.

In certain types of electron discharge tubes, such as the commercially available electron tube known as the RCA U4GB, the electrode assembly includes a tubular anode mounted between a pair of spacer plates, and a directly heated cathode in the shape of an inverted U suspended from one of the spacer plates and extending through the anode and through apertures in the other spacer plate. The electrode assembly is mounted on and electrically connected to the leads of a stem assembly closing one end of the envelope of the electron tube.

In the assembly of the type of electron tubes described, it is the practice first to mount the anode between the spacer plates by inserting extending tabs or ears of the anode through apertures in the spacer plates. Thereafter, a mount is formed by mounting the anode-spacer sub-assembly on the stem by welding the lower anode ears to some of the stern leads. The cathode is then assembled into the mount by threading the legs of the cathode through spaced apertures in the upper spacer plate, through the anode, and through apertures in the lower spacer plate. The upper bar connecting portion of the inverted Ushaped cathode is then pulled tightly against the upper spacer plate by pulling downwardly on the legs of the cathode extending beyond the lower spacer plate. The ends of the legs are thereafter welded to the stem leads to fix the cathode in place and to provide electrical connections with the cathode.

In order to facilitate the threading of the cathode legs through the apertures in the lower spacer plate, these apertures are formed large enough to receive both an anode ear and a cathode leg. During the cathode threading operation, the inside wall of the tubular anode acts as a guide for directing the leading ends of the cathode legs towards and through the aperture portions in which the anode ears are already received. Shorting of the cathode legs with the anode ears is avoided by pulling the cathode legs away from the anode ears and pressing them against edges of the apertures spaced from the anode ears. The cathode legs are held in position by bending the ends of the legs inwardly and Welding the ends of the legs to the stern leads. I

A problem associated with the above-described tube structures and method of assembly is that often, due to relative movement between the electrode assembly and the stem during further processing of the tube mount, the tension in the cathode legs is reduced and the cathode legs move within their apertures into engagement with the anode ears. Such engagement causes shorting of these electrodes and thus destroys the utility of the tube.

Tensioning devices including spring'and staking members, and the like, are known for maintaining tension in the cathode legs for preventing shorting of the cathode with the anode. The use of such devices, however, adds undesirable cost to the tube.

An object of this invention is to provide an improved electron discharge tube of the type described and a novel method of assembling the tube, wherein shorting of the cathode with the anode is prevented without extra cost to the tube.

For achieving the objects of this invention in accord- 'ice ance with a preferred embodiment of the invention, an electron discharge tube of the type described is provided wherein the lower spacer plate has apertures therein adapted to receive both an anode ear and a cathode leg. Although the size and shape of the apertures depend largely upon the size and shape of the cathode legs and anode ears, the apertures, according to a preferred embodiment, may be described as generally dumb-bell in shape. That is, the apertures have two enlarged openings connected by a portion of reduced size. The portion of reduced size is preferably just slightly smaller in width than the width of the cathode legs. The anode ears are preferably of channel or U-shaped cross section, and are received snugly within one of the enlarged portions of the apertures with the open side of the U facing the connecting portion of the apertures.

In the assembly of an electron tube according to the method of this invention, a mount is first assembled by threading the anode ears through their respective spacer plate apertures and welding the lower anode ears to the leads of a stem. The cathode legs are then threaded through the upper spacer plate apertures and into engagement with the anode walls. The cathode legs are guided by the anode walls to and through the enlarged aperture portions in the lower spacer plate in which the anode ears are received. Thereafter, each cathode leg is forced through the connecting portion of reduced size and into the other enlarged portion of the aperture. By proper selection of the size and shape of the connecting portions, the walls of the connecting portions are not broken as the cathode legs are forced thereby. Once in place in the other enlarged openings of the apertures, the cathode legs are restrained from movement into engagement with the anode ear by the walls of the connecting portions.

In the drawings:

FIG. 1 is a side elevation, partially broken away, of a tube embodying the invention;

FIG. 2 is a side elevation, partially broken away, of the mount for the tube shown in FIG. 1, and illustrates successive steps in the assembly of said mount;

FIG. 3 is a sectional view on an enlarged scale taken along line 33 of FIG. 1;

FIG. 4 is a sectional view on an enlarged scale taken along line 44 of FIG. '1; and,

FIG. 5 is a view similar to FIG. 4 and showing a modification of the invention.

A tube 10 which may be made in accordance with this invention is shown in FIG. 1. Tube 10 comprises an envelope 12 closed at its lower end by a header 14 of a stem assembly 15 having a plurality of leads 16, 17, and 18 ext-ending therethrough in vacuum tight fit. Mounted on, and electricity connected with the leads 16, 17, and 18, is an electrode assembly 20. Electrode assembly 20 includes a tubular anode 22 having extending ears 24 and 25, a pair of spacer plates 26 and 28 having apertures therethrough for receiving ears 24 and 25 in snug fit, and a directly heated cathode 30.

Cathode 30 is made from a narrow ribbon of conductive material coated with an electron emissive material. As an example, cathode 30 may be formed from a nickel all-0y coated with a conventional triple carbonate electron emitting material. The cathode 30 has an inverted U-shape and is suspended from the upper spacer plate 26. Legs 32 and 3 of the cathode extend through the anode 22, through the bottom spacer plate 28, and are Welded to a pair of leads 16, 17. The legs 32 and 34 are coated with electron emissive material, except that the emissive material is omitted from their ends 36 and 38, respectively, to facilitate welding.

Anode 22 has substantially a rectangular cross section (see FIG. 3), and ears 24, 25, which are continuations of side portions 40 of the anode, are channel or U-shaped.

For reasons described hereinafter, the channels defined by the anode ears are large enough to receive the cathode legs 32, 34 therethrough.

Upper and lower spacer plates 26 and 28 have apertures adapted to receive the anode ears 24, in snug fit therein and to permit threading of the cathode through the spacer plates.

As shown in FIG. 3, upper spacer plate 26 has spaced apart apertures 44 bridged by a bridge 46 (see FIG. 1). Each aperture 44 includes an enlarged portion 50 adapted to receive an anode ear 24 snugly therein, and an elongated portion 52 adapted to receive the cathode ribbon 3!] therethrough. The elongated portions 52 have a width slightly greater than the cathode ribbon 30 to facilitate threading of the cathode through the portions 52.

As shown in FIG. 4, lower spacer plate 28 has a pair of apertures 56 therethrough for receiving the anode ears 25 and cathode legs 32, 34. Apertures 56 each comprise an enlarged portion 58 adapted to receive the anode ears 25 in relatively snug fit, a second enlarged portion 69 adapted to receive the cathode legs 32, 34 in relatively loose fit, and a portion 62 connecting portions 58 and 6t). Connecting portion 62 preferably has a width slightly less than the width of the cathode ribbon 30.

In the assembly of the electron tube described, a subassembly comprising the anode 22 and the two spacer plates 26 and 28 is first assembled by mounting the spacer plates on opposite ends of the anode 22 by threading the anode ears 24 and 25 through the spacer plate apertures 44 and 56, respectively. As shown in FIGS. 3 and 4, the anode ears 24, 25 are received within the enlarged portions 50 and 58 of the apertures With the open sides of the ears facing the remaining portions of the apertures. Because of the snug fit of cars 24 and 25 within apertures 44 and 56, a relatively rigid sub-assembly is provided.

The anode-spacer plate sub-assembly is then mounted on the stem assembly 15 by welding the stem leads 18 to the anode ears 25.

As shown in FIG. 2, the cathode 30 is next assembled into the mount. Prior to assembly, the legs of the cathode 30 diverge more than a U-shape with parallel legs. Thus, when the cathode 30 is threaded into the apertures 44 in the upper spacer plate 26, the leading ends 36, 38 of the cathode legs engage the inside of the end walls 40 of the anode (as shown at A in FIG. 2). Because the channel formed by the anode ears are large enough to receive the cathode, as mentioned, the cathode ends are thus guided through the anode ears and through the anode ear portions 58 of the apertures 56 in the lower spacer plate 28 as the cathode 30 is pushed downwardly (as shown at B in FIG. 2).

The operator then grasps each end of the cathode legs 32, 34 extending beyond the lower spacer plate 28 and pulls the cathode downwardly until the upper portion 66 of the cathode is pressed tightly against the bridge portion 46 of the upper spacer plate 26. Thereafter, and while holding one of the cathode legs to prevent movement thereof, the operator welds the other leg (as shown at C in FIG. 2) to the upwardly extending lead 17. The other leg is then also welded to the upwardly extending lead 16.

The cathode legs 32, 34 are then forced through the connecting portions 62 of apertures 56 and into portions 60 to dispose the legs away from the anode ears (FIG. 4). To accomplish this, the operator, by means of a suitable tool, such as a tweezer, squeezes both cathode legs 32, 34 towards one another adjacent the lower spacer plate 28, thereby bending or kinking the legs 32, 34 (see FIG. 1) and at the same time snapping or forcing the cathode legs through the connecting portions 62 and into portions 60. Placing the kink 68 in the cathode legs 32, 34 serves to increase the tension in the legs and prevent movement of the cathode legs. Once the cathode legs are received within aperture portions 60, the walls of the connecting portions 62 prevent movement of the cathode legs backwardly through the connecting portions 62 and into the anode ear portions 58.

In one tube made by the method described above, the cathode ribbon 30 has a width of 39 mils, and the connecting portion 62 has a width of 37 mils. The cathode leg receiving portion 60 of apertures 56 has a Width of 55 mils and a length of 22 mils. The outside dimensions of anode ears 24, 25 are 138 by mils, and the corresponding dimensions of the anode ear receiving portions 44, 58 are by 103 mils.

FIG. 5 shows a further embodiment of this invention. In this embodiment, a two-part anode ear and cathode leg receiving aperture in the lower spacer 28 is used. Aperture 70 includes an enlarged portion 72 which receives the anode ear 25, and an elongated portion 73 which re ceives the cathode legs 32, 34. The width of portion 73 is made slightly less than the width of the cathode ribbon. Thus, after the cathode legs are passed through portions 72, the legs are forced inwardly of portions 73. The press fit between the cathode ribbon 30 and the walls of portion 73 prevent backward movement of the cathode legs toward the anode ear.

Other variations will be apparent to those skilled in the art.

What is claimed is:

1. An electron discharge device comprising an anode having an ear, a pair of spacer plates mounted on opposite ends of said anode, and a filamentary cathode having a leg within said anode, one of said spacer plates having an aperture including first and second connected portions, said first portion having a greater width than said second portion, said anode ear extending through said first portion, and said leg extending through said second portion, the width of said second portion permitting forced movement of said leg therein but preventing free movement of said leg from said second portion into said first portion.

2. An electron discharge device comprising an anode having at least one car, a pair of spacer plates mounted on opposite ends of said anode, and a filamentary cathode having at least one leg within said anode, one of said spacer plates having an aperture including first, second, and third portions of decreasing width in the order named, said third portion being disposed between said first and said second portions, said anode ear extending snugly through said first portion, said cathode leg extending through said second portion, and the width of said third portion permitting forced movement of said leg therethrough but preventing free movement of said leg from said second portion into said first portion.

3. An electron discharge device comprising an anode having a pair of ears extending from one end thereof, said ears having a U-shaped cross section, a pair of spacer plates mounted on opposite ends of said anode, a stem assembly, said anode being mounted on said stem assembly, and a U-shaped filamentary cathode within said anode, said cathode having a pair of legs extending through one of said spacer plates, said one spacer plate having a pair of apertures each including first, second, and third portions of decreasing width in the order named, said third portion being disposed between said first and said second portions, said anode ears extending snugly through said first portion of said apertures with each of said U-shaped ears opening towards said second portion thereof, said cathode legs extending through said second portion and being secured to said stern assembly, and the width of said third portion permitting forced movement of said legs therethrough but preventing free movement of said legs from said second portion into said first portion.

References Cited by the Examiner UNITED STATES PATENTS 2,115,934 5/1938 Smith 313261 X 2,625,665 l/l953 Batzle 3l3-288 X JOHN W. HUCKERT, Primary Examiner.

DAVID J. GALVIN, Examiner.

A. I. JAMES, Assistant Examiner. 

3. AN ELECTRON DISCHARGE DEVICE COMPRISING AN ANODE HAVING A PAIR OF EARS EXTENDING FROM ONE END THEREOF, SAID EARS HAVING A U-SHAPED CROSS SECTION, A PAIR OF SPACER PLATES MOUNTED ON OPPOSITE ENDS OF SAID ANODE, A STEM ASSEMBLY, SAID ANODE BEING MOUNTED ON SAID STEM ASSEMBLY, AND A U-SHAPED FILAMENTARY CATHODE WITHIN SAID ANODE, SAID CATHODE HAVING A PAIR OF LEGS EXTENDING THROUGH ONE OF SAID SPACER PLATES, SAID ONE SPACER PLATE HAVING A PAIR OF APERTURES EACH INCLUDING FIRST, SECOND, AND THIRD PORTIONS OF DECREASING WIDTH IN THE ORDER NAMED, SAID THIRD PORTION BEING DISPOSED BETWEEN SAID FIRST AND SAID SECOND PORTIONS, SAID ANODE EARS EXTENDING SNUGLY THROUGH SAID FIRST PORTION OF SAID APERTURES WITH EACH OF SAID U-SHAPED EARS OPENING TOWARDS SAID SECOND PORTION THEREOF, SAID CATHODE LEGS EXTENDING THROUGH SAID SECOND PORTION AND BEING SECURED TO SAID STEM ASSEMBLY, AND THE WIDTH OF SAID THIRD PORTION PERMITTING FORCED MOVEMENT OF SAID LEGS THERETHROUGH BUT PREVENTING FREE MOVEMENT OF SAID LEGS FROM SAID SECOND PORTION INTO SAID FIRST PORTION. 